Re: Bizarre link errors

[Keith Thompson <kst@cts.com>]

"Daniel Clarke" <clarked@aston.ac.uk> writes:
> I'm working on a project involving C and Ada, ada executables importing
> functions from C libraries.  When we try to build the executable we're
> getting a series of bizarre link errors ( included below ).  The unresolved
> externals are mostly coming from one file which does have a lot of casting
> going on which may explain the references to rtti in the linker output.
> Beyond that the errors mean nothing to me.  I think the problem is arising
> from the ada linker not linking in some core C++ library but how to solve it
> is another matter.  I've tried removing sections of code but the symbol
> references occur all over the place.
> 
> Platform is SunOs 5.6 on a sparc ultra

Interesting.  I just ran into a linking problem yesterday that
involved some of the same symbols, though I wasn't using Ada, so it
may not be exactly the same problem.

I was trying to build a large C++ software package using g++ version
2.8.1, and g++ died with an internal error while compiling one of the
source files.  I ran switched to version 2.7.2.2 and ran "make" again.
I got a linker error very similar to the one you ran into.  The
problem was that I was trying to link together object files created by
two different versions of g++.  Apparently some of the symbols
changed.  When I deleted the objects ("make clean") and ran "make"
again, it was ok.

Your problem may be a bit different, but I suspect it's also a problem
with two different versions of gcc.  The current release of GNAT is
based on a specific version of gcc (I don't remember which one).  I
suspect you're using a different version of gcc, probably a newer one,
to compile your C++ code.  (I presume you're using g++ and not Sun's
CC.)

Ideally, you should use the same version of gcc for both your Ada and
your C++ sources.  Unfortunately, the GNAT binary distribution
includes the C front end, but not the C++ front end -- and later
versions of g++ are significantly closer to complying with the C++
standard.

Whatever version of g++ you're using to compile the C++ code, you
might try invoking it on a C++ main program with the "-v" option.
This will tell you what arguments it's passing to the linker.
Manually invoking GNAT's linker with the same arguments *might* solve
your problem -- or it might silently mask a more serious one.

You might also consider writing your main program in C++ instead of
Ada, and linking with g++ rather than with GNAT's gcc (adding calls to
adainit and adafinal as appropriate).  Unlike Ada, C++ doesn't provide
a good way to allow calls from a main program in a foreign language
while guaranteeing proper initialization.  (Some Unix linkers handle
this; others don't.)

If this doesn't help, the chat@gnat.com mailing list might be more
helpful than comp.lang.ada.  Be sure to specify what version of GNAT
and of g++ you're using.

Finally, check the GNAT documentation (which I don't have handy) for
information about mixing Ada and C++.

-- 
Keith Thompson (The_Other_Keith) kst@cts.com  <http://www.ghoti.net/~kst>
San Diego Supercomputer Center  <http://www.sdsc.edu>                 <*>
Techno-geek.  Mouse bigger than phone.  Bites heads off virtual chickens.